Fuse testing terminal



Feb. 19, 1952 MONAMARA 2,586,366

FUSE TESTING TERMINAL Filed Aug. 4, 1950 ELE: E

INVENTOR. AD FQANQ JM NAMAQA A-r'ro QM ems Patented Feb. 19, 1952 UNITED STATES FATENT OFFICE 3 Claims.

This invention relates to a fuse box constructed and arranged for testing fuses therein without opening the box and more particularly to fuse testing devices mountable in a wall or door of a fuse box and accessible from the exterior of the box so that fuses in the box can be tested without opening the box.

In many house and commercial wiring systems now in use the main or buss fuses of the system are inclosed in a fuse box along with the main switches of the system and the door of such fuse box is usually sealed in closed position to be opened only by a licensed electrician or a power company employee. This is to avoid unauthorized tampering with the main fuses and switches and protect unauthorized persons from danger of electrical shock and burns as well as to protect the wiring system against overload currents that might occur incidental to improperly changing the fuses or the use of improper fuses. In many localities it is also required that even where the seal is broken and fuses tested or changed by a licensed electrician, a power company employee must be called in to inspect and reseal the box. for this service and in many cases it is found that there is nothing wrong with the main fuses but that the trouble is somewhere else in the system.

It is, therefore, among the objects of the present invention to provide an improved fuse box assembly so constructed and arranged that fuses within the box can be quickly and safely tested by means of a simple tester from outside the box and without the necessity of opening the box,

which assembly includes fuse testing devices mounted in the door or in a wall of the box in position to render it possible to make electrical contact between the prongs or terminals of a tester located entirely outside of the box and various circuit terminals located within the box without opening the fuse box, which testing devices include bodies of insulative material secured to the box to maintain the box electrically insulated from the circuit wires and terminals when fuses in the box are being tested as well as at all other times, which make no electrical contact with the circuit terminals exceot when the fuses are being tested and require positive movement by pressure of the tester prongs or terminals r against resilient forces in order to make contact for testing purposes thus avoiding any danger of accidental connection of the circuit terminals to the fuse box or to a person touching the box or thrusting objects of electrically conductive There is usually a substantial fee charged material into the testing devices, and accidental connection between different terminals in the box, which devices include in the electrically insulative portions thereof bores or openings for the reception of tester prongs or terminals and have removable closures closing these bores or openings to exclude moisture, dirt and insects from the testing devices, which devices may be mounted in an existing fuse box or incorporated original parts of a new box, and which are simple and durable in construction, economical to manufacture, easy to install and safe and effective in use.

Other objects and advantages will become apparent from a consideration of the following description and the appended claims in conjunction with the accompanying drawing wherein:

Figure 1 is a perspective view of a switch box with fuse testing devices illustrative of the invention installed therein;

Figure 2 is a fragmentary cross sectional view onan enlarged scale on the line 2-2 of Figure 1;

Figure 3 is a cross sectional view on a further enlarged scale of one of the fuse testing devices, the section plane being indicated by the line 33 of Figure 2;

Figure 4 is a transverse cross sectional view on the line l4 of Figure 5; and

Figure 5 is a diagrammatic view of a fragmentary portion of a wiring system to illustrate a method of testing fuses by the fuse testing devices of the invention.

With continued reference to the drawing, the fusebox, generally indicated at H], may be a rectangular metal box of known construction having a back wall H,-side and end walls joined to and projecting from corresponding edges of the back wall, and a door l2 hinged along one edge, as indicated at E3, to one of the side or "end walls and covering the open front of the box. At its edge remote from the hinge the door may be provided with a slotted hasp [4 receiving a staple l5 and a seal l6 may be secured to the staple to maintain the door in closed position. I

'Inside the box a block it of electrically insulative material is mounted on the back wall 5 l and carries terminals M3 for the main or buss fuses is.

Since the ordinary main circuit is a three wire circuit there would normally be three sets of fuse terminals carrying three fuses, as indicated at l 9a,'l9b and I90 in Figure 5. The switch box also normall includes a main-"switch having three blades for a three wire circuit, as indicated at a, 20b and 200 in Figure 5. This switch is usually disposed between the lead-in wires and the fuses and may be operated by a handle 2| projecting through one side of the box.

The fuse testing device of the invention is generally designated at 22 and, in the case of a fuse box of the character indicated above containing three fuses for a three wire system, six such devices, as indicated at 22a, 22b, 22c, 2211, 22c and 22f, are mounted in the door of the box, as illustrated in Figure 1.

As the devices are all substantially identical in construction, a detailed illustration and description of one only is considered sufficient for the purposes of the present disclosure.

As illustrated in detail in Figures 3 and 4, the device comprises a cylindrical, socket providing body 23 of electrically insulative material and having a coaxial bore 24 therethrough and a counterbore 25 at one end thereof. An external annular flange 26 is provided on the body 23 at the end thereof remote from the counterbore and external screw threads 2'! are provided on the body adjacent the flange.

An end closure 28, also of electrically insulative material, is disposed against the end of the body containing the counterbore and is secured to the body by suitable means, such as the screws 29. This end closure is provided with an aperture 30 smaller than and substantially coaxial with the counterbore 25.

A stem 31 of electrically conductive material is slidably received in the aperture 30 and extends through the closure 28. A head 32 is provided on one end of this stem and is slidably disposed in the counterbore 25, the stem and head together constituting a plunger, and a compression spring 33 is disposed in the counterbore between the closure 28 and the head 32 and resiliently urges the plunger toward the end of the counterbore 25,

remote from the closure 28.

As shown in Figure 5, the box contains three line terminals 34a, 34b and 340 for the three lead-in wires 35a, 35b and 35c, which may also serve as poles for the switch blades 20a, 20b and 200 respectively.

The door of the switch box is provided with three apertures registering respectively with the line terminals 34a, 34b and 340 and these apertures are of a size to receive the externally screw threaded portions of the bodies 23 of the fuse testing devices 22a, 22b and 220 respectively. The flange 26 of each such body bears on the outer side of the door I 2 surrounding the corresponding aperture, and a nut 36 is threaded onto the screw threads 21 and bears against the inner side of the door to secure the device firmly in place in the corresponding aperture in the door.

The door is also provided with three apertures respectively in registry with the fuse terminals l8a, [8b and I80 at the ends of the fuses remote from the line terminals 34a, 34b and 340 and three fuse testing devices 2201, 22c and 22 are mounted one in each of these apertures.

The devices 22 are so dimensioned that when the door of the switch box is closed the ends of the stems 3| remote from the heads 32 are spaced from the corresponding line and fuse terminals. With the switch box door still closed, by inserting a prong of atesting device into the bore 24 of a body 23 from the end of such bore exposed at the outer side of the fuse box and pressing against the head 32, the head and associated stem 3| can be moved against the force ,of spring 33 to bring the end of the stemremote from the head into electrically conductive contact with the corresponding line or fuse terminal.

A plug or cork 3'! is inserted into the end of the bore 24 of each body at the flanged end of the body to exclude dirt, moisture and insects from the device. When the devices are being used to test the fuses, these plugs are temporarily removed.

The fuses can be tested with a simple tester comprising a light bulb socket, a bulb in the socket, two flexible leads extending from the socket and two insulated prongs connected one to each lead at the end thereof remote from the socket.

One method of testing the fuses with such a tester will now be explained in connection with Figure 5.

To test the fuse [9a one prong of the tester may be inserted in the bore of the device 22d and the other in the bore of the device 22b. The fuse Isa and the tester will now be in series with each other between the hot line 35a and the ground or neutral wire 35?) and, if the fuse is good, the light bulb of the tester will be illuminated. If the light bulb is not illuminated the prong in device 22d may be moved to device 220. to test the circuit between the lead-in wires 35a and 35b. If the bulb is now illuminated the evidence is substantially conclusive that the fuse l9a is burnt out. The line 350 can be tested across the devices 220 and 2222, the fuse l across the devices 22; and 22b and the fuse I9b across the devices 22c and 220, or 226 and 220. Other testing methods will readily occur to those skilled in the art.

The invention may be embodied in other specific forms Without departing from the spirit or essential characteristics thereof. The present embodiment is, therefore, to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are, therefore, intended to be embraced therein.

What is claimed is:

1. In combination with a fuse box having a door, fuse terminals in said box, fuses in said fuse terminals and line terminals in said box, means for testing said fuses without opening said box comprising insulated testing devices mounted in a wall of said box and disposed one in alignment with each of said line terminals and one in alignment with each fuse terminal remote from the corresponding line terminal, each of said testing devices having a bore opening to the outside of said box for receiving a tester prong and a plunger slidable in said bore and spring-urged away from the corresponding line or fuse terminal, said plunger being movable into electrically conductive contact with the associated line or fuse terminal by pressure of a tester prong thereon.

2. In combination with a fuse box, fuse and line terminals in said box and a fuse box door having apertures therein in alignment with selected fuse and line terminals, fuse testing devices mounted one in each of said apertures and each comprising a body of electrically insulative material secured at one end to said door and having a bore opening to said one end to receive a tester prong, a plunger of electrically conduc" tive material slidably mounted in said body and projecting from the other end of the latter, and a spring in said body resiliently holding said plunger out of contact with the associated line or fuse terminal, said plunger being movable against the force of said spring into electrically conductive contact with the associated line or fuse terminal by pressure of a tester prong thereon.

3. A fuse testing device mountable in a fuse box wall for testing fuses in the box comprising an elongated body of electrically insulative material having a bore extending therethrough and a counterbore in one end thereof, said body having an outwardly projecting flange at its other end and a screw threaded portion adjacent said flange, a nut threaded onto said screw threaded portion for clamping a fuse box wall between itself and said flange, a closure secured to said one end of said body and having an aperture therethrough, a plunger of electrically conductive material including a stem slidably mounted in the aperture in said closure and extending through the latter and a head on one end of said 6 stem and slidably received in said counterbore, and a compression spring disposed in said counterbore between said closure and said head and resiliently urging said plunger toward the end of said counterbore remote from said closure, said counterbore providing at its juncture with said bore an annular shoulder constituting an abutment for said head to maintain the latter within said counterbore against the force of said spring.

FRANCIS J. McNAMARA.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,457,671 Rector June 5, 1923 1,585,485 Gernsback May 18, 1926 1,933,506 Noyes Oct. 31, 1933 

